Transient QWindows centered; default-constructed geometry

Default-constructed geometry does not mean put the window at 0,0,
and it does not mean center the window on the screen: it means
let the window manager position the window.  If the window is
explicitly positioned at 0,0 though, that is a higher priority
than the transient hint; without this change, the transientFor property
had no effect.  On X11, transient means use center "gravity" to
make the transient window exactly centered.  But the user can still
override the geometry of a transient window, as with any window.
On OSX and Windows, neither transient window functionality nor smart
initial positioning are provided, so a window with no position set
will be centered on the screen, and a transient window will be put
at the center of its transientParent.

Change-Id: I4f5e37480eef5d105e45ffd60362a57f13ec55f5
Task-number: QTBUG-26903
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>

1 files changed, 15 insertions, 2 deletions

diff --git a/src/gui/kernel/qwindow.cpp b/src/gui/kernel/qwindow.cpp
index 2fcad5706f..2a2e30634a 100644
--- a/src/gui/kernel/qwindow.cpp
+++ b/src/gui/kernel/qwindow.cpp
@@ -126,6 +126,18 @@ QT_BEGIN_NAMESPACE
     and can keep rendering until it isExposed() returns false. To find out when
     isExposed() changes, reimplement exposeEvent(). The window will always get
     a resize event before the first expose event.
+
+    \section1 Initial geometry
+
+    If the window's width and height are left uninitialized, the window will
+    get a reasonable default geometry from the platform window. If the position
+    is left uninitialized, then the platform window will allow the windowing
+    system to position the window. For example on X11, the window manager
+    usually does some kind of smart positioning to try to avoid having new
+    windows completely obscure existing windows. However setGeometry()
+    initializes both the position and the size, so if you want a fixed size but
+    an automatic position, you should call resize() or setWidth() and
+    setHeight() instead.
 */
 
 /*!
@@ -962,7 +974,7 @@ void QWindow::setY(int arg)
 void QWindow::setWidth(int arg)
 {
     if (width() != arg)
-        setGeometry(QRect(x(), y(), arg, height()));
+        resize(arg, height());
 }
 
 /*!
@@ -972,7 +984,7 @@ void QWindow::setWidth(int arg)
 void QWindow::setHeight(int arg)
 {
     if (height() != arg)
-        setGeometry(QRect(x(), y(), width(), arg));
+        resize(width(), arg);
 }
 
 /*!
@@ -1095,6 +1107,7 @@ void QWindow::setGeometry(int posx, int posy, int w, int h)
 void QWindow::setGeometry(const QRect &rect)
 {
     Q_D(QWindow);
+    d->positionAutomatic = false;
     if (rect == geometry())
         return;
     QRect oldRect = geometry();